Zugzwang is a position where a player would love to pass — but the rules force them to move, and every move makes things worse. It's most decisive in the endgame.
With few pieces on the board, many positions are balanced only because it's not your turn. Force the opponent to move and the balance tips. In the middlegame there's almost always a useful waiting move; in the endgame there often isn't.
The opposition — kings facing each other with one square between them — is really a way of putting the opponent in zugzwang. The side not to move holds the opposition, so the other king must step aside and give ground. That's how you escort a pawn to promotion.
A 'waiting move' (often a quiet king or pawn move that keeps your structure) hands the obligation to move back to your opponent. Triangulation — manoeuvring your king to reach the same position but with the opponent to move — is the classic technique.
Ask: if I could pass right now, would I want to? If yes, look for a way to force your opponent into the same wish. That's the essence of winning with zugzwang.